The invention is directed to a process for the production of pyridine substituted in the 2- and 3-positions by aromatic or heteroaromatic groups. These substituted pyridines are important intermediate products for the production of medicines, plant protective agents and synthetic resins.
It is known to produce pyridines having aromatic substituents in the 2- and 3-positions from ketones, namely, 2,3-diphenyl pyridine from desoxybenzoin and 2-benzyl-3-phenyl pyridine from 1,3-diphenylacetone. The ketone for this purpose is first converted to the enamine, this reacted with 3-bromo-propylamine hydrobromide in dimethyl formamide to the tetrahydropyridines and these finally dehydrogenated in the presence of palladium catalyst to the pyridines (Org. Chem. Vol. 28 (1963) pages 3468 to 3473). In the case of the production of 2,3-diphenyl pyridine from desoxybenzoin this can also be reacted with 3,3-diethoxy-1-dimethylamino-1-propene to form 5-dimethylamino-1,2-diphenyl-2,4-pentadien-1-one and this reacted with triethyloxonium tetrafluoroborate and further with dimethylamine to 5-dimethylamino-N,N-dimethyl-1,2-diphenyl-2,4-pentadieniminium-tetrafluoro borate and finally this converted into the 2,3-diphenyl pyridine by heating in an ammonium chloride-ammonia solution (Liebigs Ann. Chem. 1975 pages 874 to 900).
These processes are little suited for use in producing the substituted pyridines on an industrial scale. They are expensive and cumbersome to handle. Besides several of the necessary reagents are only available with difficulty.